TY - JOUR
T1 - Microbially mediated organomineralization in the formation of ooids
AU - Diaz, Mara
AU - Eberli, Gregor P
AU - Blackwelder, Patricia
AU - Phillips, Brian
AU - Swart, Peter K.
N1 - Funding Information:
We thank S. Ahearn for scanning electron microscope image processing and G. MacKenzie for proofreading. Special thanks to E. C. Rankey, B. Jones, and an anonymous reviewer for insightful comments. This research was funded by the CSL–Center for Carbonate Research at the University of Miami (Florida, USA).
Publisher Copyright:
© 2017 Geological Society of America.
PY - 2017/9/1
Y1 - 2017/9/1
N2 - While ooids have been significant components of many shallowwater carbonates throughout Earth's history, their abiotic or biotic origin has been much debated. Herein, we evaluate ooids from five locations in the Bahamas, where ooids are actively forming, and where ooids harbor a highly diverse microbial community with capabilities for carbonate precipitation. Using scanning electron microscopy (SEM), we identify well-preserved microbial assemblages and provide compelling evidence of biogenic signatures intrinsically related to organomineralization, including extracellular polymeric substance (EPS) exudates from biofilm-forming bacteria and diatoms; imprints of EPS degradation by heterotrophic bacteria; amorphous calcium carbonate (ACC) precipitates within microdomain areas of biofilm EPS; and extracellular precipitates on bacterial cells. As revealed by nuclear magnetic resonance and SEM imaging, ACC plays a formative role in the development of aragonite crystals in ooids. Contrary to the classical nucleation theory, aragonite mineralization in ooids occurs through prenucleation of ACC, where the intimate association between ACC and EPS and microbes suggests that ACC precipitates are biomediated. These findings argue for a new conceptual model for ooid accretion that includes a biomediated ACC metastable phase.
AB - While ooids have been significant components of many shallowwater carbonates throughout Earth's history, their abiotic or biotic origin has been much debated. Herein, we evaluate ooids from five locations in the Bahamas, where ooids are actively forming, and where ooids harbor a highly diverse microbial community with capabilities for carbonate precipitation. Using scanning electron microscopy (SEM), we identify well-preserved microbial assemblages and provide compelling evidence of biogenic signatures intrinsically related to organomineralization, including extracellular polymeric substance (EPS) exudates from biofilm-forming bacteria and diatoms; imprints of EPS degradation by heterotrophic bacteria; amorphous calcium carbonate (ACC) precipitates within microdomain areas of biofilm EPS; and extracellular precipitates on bacterial cells. As revealed by nuclear magnetic resonance and SEM imaging, ACC plays a formative role in the development of aragonite crystals in ooids. Contrary to the classical nucleation theory, aragonite mineralization in ooids occurs through prenucleation of ACC, where the intimate association between ACC and EPS and microbes suggests that ACC precipitates are biomediated. These findings argue for a new conceptual model for ooid accretion that includes a biomediated ACC metastable phase.
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U2 - 10.1130/G39159.1
DO - 10.1130/G39159.1
M3 - Article
AN - SCOPUS:85028499894
VL - 45
SP - 771
EP - 774
JO - Geology
JF - Geology
SN - 0091-7613
IS - 9
ER -